Burner for analytical procedures



July 21, 1964 D. c. HOEL ETAL BURNER FOR ANALYTICAL PROCEDURES 2 Sheets-Sheet 1 Filed Sept. 26, 1961 IN VEN TORS n \N NN July 21, 1 4 D. c. HOEL ETAL BURNER FOR ANALYTICAL PROCEDURES 2 Sheets-Sheet 2 Filed Sept. 26, 1961 4 mm s M m m N W L Wm M N MW 5 V. A & a. k \N\ v g ||l IQ! R Q 1 t\\.\- I. .1\\n .NN N a .1 Q \r R R v w 1 mm 3 Q R R v w W\ N ATTORNEY United States Patent 3,141,741 BURNER FOR ANALYTICAL PROQEDURES Dean C. Hoei, Verona, and Beniarnin M. Wedner, Pittsburgh, Pa, assignors to Gulf Research 8; Development Company, Pittsburgh, Pa, a corporation of Delaware Filed Sept. 26, 196i, Ser. No. 140,818 Claims. (Cl. 2325$) This invention relates to a gas burner useful in certain combustive analytical procedures and more particularly to a laboratory burner useful to effect combustion of samples to be analyzed in oxidative and/ or pyrohydrolytic analytical techniques.

The quantitative analytical determination of substances such as halogens, sulfur and certain other elements present in organic chemical compounds and in some inorganic compounds frequently requires preliminary destruction of the chemical residues attached to the above elements, usually by oxidation in the instance of organic chemical residues, and by a combination of oxidation and hydrolysis, or pyrohydrolysis, in the case of inorganic chemical residues. A number of oxidative and pyrohydrolytic analytical techniques involving indirect combustion of the samples subjected to analysis have been proposed, but all of these previously proposed methods have disadvantages as applied to routine analysis, either from the standpoint of cumbersome and/or costly equipment, tedious techniques, and time consumed. The latter factors are especially important when the analysis in question is to be used for purposes of process control, as in these instances analytical results are desired in the shortest pos sible time.

In recent years improved oxidative and/or pyrohydrolytic analytical techniques for the analysis of halogens and the like have been developed involving direct combustion of the unknown sample by means of a special gas burner constructed entirely of quartz. This burner has been described in Angew. Chem., 69, 530 (1957). In accordance with the improved direct combustion procedures, the flame of the aforesaid burner provides a combination of intense heat and an excess of oxygen required for rapid and complete destruction of the chemical bonds between the substance being analyzed for and the chemical residue attached thereto. The burner flame also provides a supply of water vapor when this is required for purposes of pyrohydrolysis of inorganic materials. While the improved direct combustion methods referred to have eliminated many of the disadvantages of previous oxidative and pyrohydrolytic analytical techniques, these disadvantages have been supplanted by other disadvantages attributable to the burner itself. For example, the burner, being formed entirely of quartz by glass-blowing techniques, is not adapted to volume production because of its integral quartz construction, its complexity of design and the close tolerances required in the burner nozzle. As a result of these factors, months of delay have been experienced in obtaining these burners. The quartz burners are also disadvantageous in that they frequently do not produce a flame having optimum analytical characteristics. That is, these burners, being formed manually, are occasionally geometrically imperfect-sometimes even to the naked eyewhereby they produce non-symmetrical flames during combustion of liquid samples owing to imprecise, nonuniform spacing of burner nozzle parts. A non-symmetrical flame is objectionable in that substantial temperature differences can exist in such a flame, whereby incomplete combustion and/or pyrohydrolysis of sample may occur, thereby adversely affecting the accuracy of the analytical results. A further disadvantage of the quartz burners is that they are subject to severe chemical attack during combustion of certain types 3,141,141 Ice Patented. July 21 1964 of compounds. Under such corrosive conditions it has been found that the life of a single quartz burner may be no more than about 15 analyses, after which the entire burner must be discarded. It has further been found that the use of the quartz burners is limited in the case of liquid samples to a rather narrow range of physical properties, i.e., viscosities, heat of combustion, molecular Weight, etc., because of the extremely close spacing between parts of the burner nozzles. Also, every part of the quartz burners is subject to breakage. In the event of breakage of any important part of the burner, the entire burner must be discarded.

The present invention relates to an improved analytical burner construction comprising a separable assembly of several elements, each adapted to be mass-produced with close control of tolerances and spacing, whereby an improved fiame is produced. The burner assembly, being separable, can be disassembled to facilitate cleaning of the extremely smaller burner orifices. Moreover, the entire burner need not be discarded in the event that one component requires replacement. In addition, the material from which the burner, or individual components thereof, or parts of such components are fabricated can be selected for optimum properties for the particular application involved. Finally, because of its increased flexibility, the improved burner can be used with liquid samples having a wide range of physical properties. We have found that a burner having the above-indicated characteristics can be obtained by the provision of a coaxially mounted, nested series of separable tubular ducts of graduated diameter, including a primary oxidant gas duct, a secondary oxidant gas duct, and a fuel gas duct. Each of the gas ducts has a discharge end and also a base end. The ducts are spaced apart at their discharge ends so as to form a graduated series of concentric, annular discharge orifices positioned about a centrally positioned discharge orifice that is substantially coterminous therewith. Each of the aforesaid gas ducts is provided with an inlet orifice at its base end for introduction of the appropriate gas. Each of the ducts other than the centrally positioned duct inthe aforesaid series is removably mounted at its base end upon the base of the next smaller duct in the series. Each of the aforesaid ducts is formed from an impact-resistant material selected to withstand the conditions to be encountered in service. Machinable, heat and corrosion-resistant metals such as stainless steel are highly suitable materials of construction for purposes of this invention, but other materials can be used. The abovedescribed structure suffices for purposes of pyrohydrolytic analytical techniques, but for purposes of a burner that is suitable as either a pyrohydrolytic burner or an oxidative combustion burner, the nested series of ducts that form the burner structure of this invention will also include a sample duct. This structure is preferred because of its greater flexibility. Where flexibility with respect to liquid sample viscosity is important, the mounting between the base of the centrally positioned smallest duct and the base of the next larger duct in the series is adjustable so as to control at least one of the depth to which the centrally positioned discharge orifice is recessed. In this modification we prefer that the discharge end of such next larger duct be tapered inwardly toward the flow axis, and that the outer surface of the centrally positioned smallest duct be correspondingly tapered inwardly, so as to provide an inwardly directed annular orifice, or annulus, whose radial spacing is variable with the position of the smallest duct. Where additional flexibility in analyzing diflicultly combustibie liquids and/ or very viscous liquids is desired, we prefer that the sample duct be provided with a pair of inlet orifices at its base end whereby such very viscous and/ or diflicultly combustible liquid samples can be introduced through one of said orifices and a more easily combustible and/or a less viscous solvent can be introduced through the other inlet orifice with the maximum sample:solvent ratio and at the maximum sample rate consistent with a good quality burner flame.

Referring now briefly to the drawings, in FIGURE 1 there is illustrated a sectional view in side elevation of one modification of the improved gas burner of this in vention. FIGURE 1(a) is an end view of the discharge end of the burner nozzle of FIGURE 1. In FIGURE 2 there is shown in side elevation a second modification of the burner of this invention having additional flexibility as described above. FIGURE 2(a) is an end view of the burner nozzle of FIGURE 2. In FIGURE 3 there is illustrated an analytical combustion train embodying a gas burner of this invention. In all of the figures of drawing, like numerals denote the same or similar elements.

Referring to FIGURE 1 in greater detail, the letter A designates the over-all burner structure. Numerals 2, 4, 6, and 8 denote the series of coaxially mounted, nested, separable tubular ducts of graduated diameter. These ducts are formed from an impact-resistant material selected to withstand temperature and corrosion conditions to be encountered in service. Excellent results are obtainable with stainless steel, but other non-frangible, machinable, heatand corrosion-resistant materials such as Monel metal, Inconel, and even organic plastics such as epoxy resins can be used. Surprisingly, the use of metals in fabricating the burner parts has been found not incompatible with the high burner flame temperatures and the use of quartz combustion chambers, notwithstanding the consequent necessity for a gas-tight joint between the burner nozzle and the combustion chamber. Ducts 2, 4, 6, and 8 are spaced apart at the discharge ends so as to form a graduated series of concentric annular discharge orifices 1t), 12, and 14 lying in substantially the same plane about a centrally positioned discharge orifice 16 that is slightly recessed from such plane. Although in the usual case, a recessed position of orifice 16 is considered to produce a superior flame, such recessing is not absolutely necessary, and the orifice 16 can be in the same plane as the other orifices or it may project somewhat beyond such other orifices. Numeral 2 denotes a tubular duct of relatively small diameter which in this instance is adapted to provide a flow of primary oxidant gas such as oxygen or air from a source, not shown, to the discharge end or nozzle of the burner. Tubular duct 2 is provided with a centrally positioned discharge orifice 16 which is preferably somewhat constricted relative to the inner diameter of the duct itself, in order to increase gas velocity in the vicinity of the nozzle.

Tubular duct 2 has a threaded collar member 18 mounted thereon to form a base member for the burner assembly. The threads of base member 18 together with the corresponding threads at the base of base member 20 of the next larger tubular duct 4 form an adjustable mounting or fitting 22 by means of which there can be controlled the relative position of discharge orifice 16 and/or the radial spacing between the discharge end of duct 2 and the discharge end of the next larger duct 4. This adjustment is conveniently controlled by the thickness of spacing means 24, which preferably comprises a washer formed from a heat resistant, relatively soft material that is machinable to close tolerances, such as copper metal. Numeral 26 denotes an inlet orifice at the base end of duct 2 for introduction into the burner of primary oxidant gas.

Numeral 4 in the apparatus illustrated in FIGURE 1 refers to a sample duct, that is, a duct adapted to conduct a flow of sample to the burner flame, said duct having an inwardly tapered discharge end that together with the correspondingly inwardly tapered discharge end of primary oxidant duct 2 forms the annular orifice 19 directed inwardly towards the axis of flow from discharge orifice 16 of primary oxidant gas duct 2. The inside walls of sample duct 4 may contain spiral grooves or rifling, or vanes, or equivalents of either, if desired, particularly at the discharge end of the duct, so as to provide a swirling motion to the sample and to facilitate intermixture with the oxidant gas. The radial spacing between the inner surface of the discharge end of sample duct 4 and the outer surface of the discharge end of primary oxidant duct 2 is uniform at all parts of the annulus so as to insure equal distribution of sample around the entire circumference of the burner flame. The relative advancement of discharge orifice 16 and the magnitude of the radial spacing between the inwardly tapered inner surface of the discharge end of sample duct 4 and the correspondingly tapered outer surface of the discharge end of primary oxidant duct 2 are conveniently increased or decreased by the substitution of relatively thicker or thinner copper washers for spacing means 24.

Sample duct 4 has an enlarged base member 20 at its base end, the inner surface of which, together with the corresponding outer surface of primary oxidant duct 2, forms a sample receiving chamber 28 at the base end of duct 4. Chamber 28 is provided with an inlet orifice 38 through which the liquid sample that is to be analyzed can be introduced. As indicated above, base member iii of sample duct 4 is provided with a threaded fitting at its base end which together with the correspondingly threaded fitting of base member 13 of primary oxidant duct 2 forms the adjustable mounting 22 referred to previously. Base member 20 is also provided with a threaded fitting at its forward end which together with the correspondingly threaded fitting at the base end of base member 32 of the next larger duct 6 forms an adjustable mounting 34. Numeral 35 denotes another spacing memher like member 24, preferably a copper washer machined to a thickness such as to cause the discharge end of sample duct 4 to terminate in the same plane with the discharge end of the next larger duct 6.

Numeral 6 refers to a still larger tubular duct in the nested series previously referred to, said duct encasing sample duct 4 and primary oxidant duct 2. Duct 6 in the illustrated apparatus is adapted to provide a flow of fuel gas from a source, not shown, to the burner flame. Hydrogen is the preferred fuel gas, but other fuel gases such as methane, propane, or city gas can be used. Fuel gas duct 6 is provided with an inwardly tapered discharge end, coterminous with the discharge end of sample duct 4, spaced apart at its discharge end from the correspondingly inwardly tapered discharge end of sample duct 4, so as toprovide a second annular discharge orifice 12 lying in the same plane as annular discharge orifice 10 and concentric therewith and with discharge orifice 16, whereby the fiow of fuel gas is directed inwardly towards the axis of flow from discharge orifice 16. Again, the radial spacing of the annular discharge orifice 12 is substantially equal at all parts of the annulus, whereby substantially equal distribution of fuel gas to all parts of the burner flame is obtained. Fuel gas duct 6 is also provided with an enlarged base member 32 whose inner surface together with the corresponding outer surface of sample duct 4 forms a fuel gas receiving chamber 36 at the base end of duct 6. Chamber 36 is provided with an inlet orifice 38 by means of which a fuel gas such as hydrogen can be introduced into the fuel gas duct 6. Base member 32 is provided at its base end with a threaded fitting which, together with the correspondingly threaded fitting on the forward end of base member 2% of sample duct 4, forms a separable mounting 34. Base member 32 is also provided at its forward end with a threaded fitting which, together with the correspondingly threaded fitting at the base end of the base member 40 of the next larger duct 8, forms a separable mounting 42 between duct 8 and duct 10.

Numeral 8 denotes a fourth duct of still larger diameter encasing fuel gas duct 6, sample duct 4, and primary oxidant gas duct 2. Duct 8 is adapted to provide a secondary flow of an axidant gas such as oxygen or air from a source, not shown, to the discharge end of the burner A and thence to the burner flame. The discharge end of duct 8 is spaced apart from and coterminous with the discharge end of fuel gas duct 6, thus forming a third, annular discharge orifice 14 lying in the same plane as annular discharge orifices 10 and 12, and concentric therewith and with discharge orifice 16. The radial spacing between the discharge ends of ducts 8 and 6 is substantially uniform at all regions in the annulus so as to provide a substantially uniform flow of secondary oxidant gas around the entire circumference of the burner flame. The outer surface of the discharge end of duct 8 is tapered inwardly to match the corresponding standard tapered female join-t 44 of the quartz combustion chamber, not shown, of the combustion train. The secondary oxidant gas duct 8 is provided with a collar member 46 at the base of the tapered joint 44, said collar abutting against the end of joint 44 and forming a gas-tight seal therewith. A second collar member 48 is formed integrally with duct 8 and acts as a support for hook members 50 and 52 which in turn act as supports for spring members, not shown, engaging corresponding hook members, not shown, on the quartz combustion chamber, not shown, so as to insure maintenance of a gas-tight seal between the burner A and the combustion chamber. Duct 8 is provided with an enlarged base member 40 whose inner surfaces together with the corresponding outer surfaces of fuel gas duct a form a secondary oxidant gas receiving chamber 54 at the base end of duct 8. Receiving chamber 54 is provided with an inlet orifice a through which a flow of secondary oxygen from a source not shown is introduced. Secondary oxidant gas duct 8 is provided with a threaded fitting at its base end which together with the correspondingly threaded fitting on the forward end of base member 32 of fuel gas duct 6 forms a separable connection 42 whereby base member 40 is removably mounted upon base member 32. Numeral 53 denotes a spacing member, again preferably a copper washer machined to a thickness such as to make the discharge end of secondary oxidant gas duct 8 coterminous with the discharge end of fuel gas duct 6 and the discharge end of sample duct 4.

Referring now to FIGURE 2, there is shown a modification B of the burner of this invention having superior flexibility of usage. In this figure it will be noted that sample receiving chamber 28 is provided with an auxiliary inlet orifice 60 for use in the combustion of very viscous analytical samples such as mineral oil or motor oil or diflicultly combustible materials such as benzene or other highly aromatic substances. In this modification an easily combustible, non-viscous solvent such as isooctane is introduced from vessel 62 through line 64, valve 66, and inlet orifice 30, instead of the sample to be analyzed as in the burner modification A shown in FIGURE 1. After adjustment of the flow of primary oxidant gas, secondary oxidant gas and solvent, relative to fuel gas flow, to obtain the maximum rate of flow of solvent consistent with good analytical flame quality, the liquid sample to be analyzed, comprising a material that is too viscous to pass through the burner without dilution and/ or that is too diflicult to burn completely without dilution with a more combustible solvent, is introduced into sample receiving chamber 28 from vessel 68 through stopcock '70, valve 72, and/ or auxiliary inlet orifice 60. The rate of flow of liquid from vessel 68 is gradually increased to the maximum rate consistent with good burner flame quality. In this way the maximum rate of combustion of unknown sample with minimum introduction of extraneous materials is achieved. When the burner of FIGURE 2 is to be employed similarly as the burner of FIGURE 1, auxiliary inlet orifice 60 can simply be sealed off by closing valve 72. It will be noted that sample receiving chamber 28 of burner B is of relatively small volume relative to the other receiving chambers 36 and 54 of the same burner in order to minimize the amount of solvent that must be flushed through the chamber after introduction of the sample to be analyzed has been completed. In addition, in FIGURE 2 the tapered discharge end of secondary oxidant gas duct 8 is provided with a pair of annular grooves 72 and 74 in which are seated a pair of 0- rings 76 and 78 formed of a relatively inert, resilient material, such as neoprene, to provide a gas-tight seal between such tapered surface and the correspondingly tapered joint 44 of the combustion chamber, not shown.

In FIGURE 3 there is shown an over-all analytical train of which the burners of this invention form subcombinations. In this figure, wherein the burner of FIGURE 1 is employed as indicated, numeral 90 refers to a hydrogen gas cylinder connected to the fuel gas inlet 38 of burner A by means of line 100. Hydrogen gas flow to inlet 38 is controlled by valve 86. Numeral 88 denotes an oxygen gas cylinder which acts as the source of primary and secondary oxidant gas. Oxygen cylinder 83 is connected to the inlet orifice 26 of primary oxidant gas duct 2 by means of line 1%. A part of the oxygen flowing through line M92 is by-passed around inlet orifice 26 through line 104 to the inlet orifice 56 of the secondary oxidant gas duct 8. The total rate of oxygen flow to the burner A is measured by flow meter 94-, and the flow through the respective lines 102 and 1% is regulated by valves 84 and 92. Vessel 106 forms a source of the sample to be analyzed, the rate of whose flow into burner A is controlled by valve 98. Numeral 96 denotes a water jacketed quartz combustion chamber and numeral 108 refers to an absorber chamber adapted to absorb the material being analyzed for. Numeral 110 denotes a condenser. Numeral 112 refers to a liquid trap submerged in an ice bath, numeral 82 refers to a flow meter adapted to measure rate of gas flow and numeral indicates a source of vacuum, not shown, to reduce the pressure in the combustion train downstream of the combustion burner.

In a specific embodiment utilizing a burner constructed of type 304 stainless steel as indicated in FIGURE 1, where the discharge orifice 16 is recessed about 0.005 inch from the plane of annular orifices 10, 12, and 14, where the diameter of orifice 16 is 0.026 inch and the width of the radial space of annular orifice 10, that is, onehalf the clearance on the diameter between duct 4 and duct 2, is about 0.0015 inch, the width of the radial space of annular orifice 12 is about 0.005 inch and the width of the radial space of annular orifice 14 is about 0.0175 inch, and using an absorber containing about 15 ml. of approximately 0.1 N sodium hydroxide solution, and a fluoridecontaining liquid sample, a vacuum is applied to the system by means of source 80 and regulated to permit a flow rate of 1200 liters of gas (air) per minute through flow meter 82 before inserting burner A into the assembly. With valves 84 and 86 closed, the reducing valves on the oxygen and hydrogen cylinders 88 and are regulated to permit discharge of gas at 4 p.s.i.g. The hydrogen valve 36 is opened slightly and the burner ignited. With valve 92 fully open valve 84 is adjusted to permit a flow of about 1000 liters of oxygen per hour through flow meter 94. Final adjustment of oxygen flow at this rate is made while simultaneously adjusting the hydrogen flow rate to produce a flame about one centimeter in length. The tapered end 45 of burner A is then inserted in the correspondingly tapered joint 44 of combustion chamber 96, and the hydrogen flow is increased to produce a flame 4 to 5 centimeters in length. By means of valve 92, excess oxygen passing through the burner is decreased causing more oxygen to jet through the center orifice 16 of the burner. The sample is then introduced to the burner flame by opening valve 98. After combustion of the sample is complete, the hydrogen cylinder valve is closed, the burner is removed from the assembly, and the oxygen valve is closed. The vacuum is then disconnected, and the contents of the absorber is filtered through Whatman No. 41 filter paper. Fluorides are then determined spectrophotometrically without prior distillation.

Many modifications and variations of the invention as herein described will suggest themselves to those skilled in the art, and resort may be had to such modifications and variations without departing from the spirit and scope of the invention. Accordingly, only such limitations should be imposed as are indicated in the claims appended hereto.

We claim:

1. A gas burner comprising a coaxially mounted, nested series of separable tubular ducts of graduated diameter including at least a primary oxidant gas duct, a secondary oxidant gas duct, a sample duct positioned between the primary and secondary oxidant gas ducts and a fuel gas duct, each having a discharge end and a base end, said ducts being spaced apart at their discharge ends and forming a graduated series of concentric, annular discharge orifices lying in substantially the same plane about a centrally positioned discharge orifice, each or" said ducts being provided with an inlet orifice at its base end for introduction of one of said primary oxidant gas, said secondary oxidant gas, said sample, and said fuel gas, each of said ducts other than the central positioned duct of said series being removably mounted at its base end upon the base of the next smaller duct in the series, said ducts being formed from impact-resistant material that is resistant to corrosion under service conditions of the burner.

2. The burner of claim 1 where the sample duct is provided with a pair of separate inlets at its base endf 3. The burner of claim 1 Where the mounting between the base of the smallest duct in the series and the base of the next larger duct in the series is adjustable so that the relative position of the discharge orifice of the smallest duct in the series can be varied.

4. A gas burner comprising a coaxially mounted, nested series of tubular ducts of graduated diameter, said series including at least a primary oxygen duct, a fuel gas duct, and a secondary oxygen duct, a first member of said series of ducts being a centrally positioned tubular duct of relatively small diameter having a discharge end provided with an axial discharge orifice and having a base end provided with an inlet orifice, a second member of said series being a tubular duct of greater diameter than said first duct and encasing said first duct, said second duct having an open discharge end and being spaced apart'from said first duct at its discharge end and forming an annular discharge orifice about the discharge end of said first duct, said second duct also having a base end provided with an inlet orifice, means for removably connecting the base of said second duct and the base of said first duct, whereby the base of said second duct is supported by the base of said first duct, a third tubular duct of greater diameter than said second duct and encasing said second duct, said third duct having an open discharge end substantially coterminous with the discharge end of said second duct and being spaced apart from said second duct at its discharge end and forming an annular discharge orifice about the same, said third duct also having a base end provided with an inlet orifice, said base end being removably mounted upon the base-of said second duct, each of said ducts being formed from a corrosion-resistant metal, said series of ducts further including a tubular sample duct, said means for removably mounting the base of said second duct and the base of said first duct comprising the base of said sample duct that is removably mounted on the base of said first duct and that has mounted thereon the base end of said second duct, said sample duct being of greater diameter than said first duct and encasing the same and being of less diameter than said second duct and being encased by the same, said sample duct having an open discharge end substantially coterminous with the discharge end of said second and third ducts and being spaced apart from said first duct at its discharge end and forming concentric annular orifices therewith, said sample duct also having an inlet orifice at its base end, and means for varying the distance beyond the discharge end of the first duct to which the sample duct extends.

5. A gas burner comprising a coaxially mounted, nested series of tubular gas ducts including a centrally positioned primary oxidant gas duct of relatively small diameter and having a discharge end provided with a restricted axial discharge orifice, said primary oxidant gas duct also having a base and at least one inlet orifice at the base end of said duct, said base being provided with a fitting adapted removably to engage the base member of the next larger duct in the series, a sample duct of greater diameter than said primary oxidant gas duct and encasing the same, said sample duct having an open discharge end and being spaced apart from said primary oxidant gas duct at its discharge end and forming an annular discharge orifice about the discharge end of said primary oxidant gas duct, said annular discharge orifice being directed inwardly toward the axis of flow from the discharge orifice of said primary oxidant gas duct, said sample duct also having a base provided with a fitting for removably engaging the corresponding fitting of the base of said primary oxidant gas duct and with a fitting removably to engage the base member of the next lar er duct in the series, spacing means between the base of said primary oxidant gas duct and the base of said sample duct for controlling the width of said annular orifice and for controlling the distance to which the sample duct extends beyond the discharge orifice of the primary oxidant gas duct, a fuel gas duct of greater diameter than said sample duct and encasing the same, said fuel gas duct having an open discharge end substantially coterminous with the discharge end of said sample duct, said fuel gas duct being spaced apart from said sample duct and forming an annular discharge orifice about the discharge end of said sample duct, said annular orifice being directed inwardly toward the axis of flow from the discharge orifice of the primary oxidant gas duct, said fuel gas duct also having a base provided with a fitting adapted removably to engage the corresponding fitting of the base or" the sample duct and with a fitting adapted removably to engage the base member of the next larger duct in the series, and a secondary oxidant gas duct of greater diameter than said fuel gas duct and encasing the same, said secondary oxidant gas duct having an open discharge end substantially coterminous with the discharge end of the fuel gas duct, said secondary oxidant gas duct being spaced apart from said fuel gas duct and forming an annular discharge orifice about the discharge end of said fuel gas duct, said secondary oxidant gas duct also having av base provided with a fitting adapted to engage the corresponding fitting of the fuel gas duct, said secondary oxidant gas duct also having an inlet orifice at its base end, the Width of the radial spacing between the discharge ends of said ducts being uniform throughout each annular orifice so as to provide uniform flow about the entire circumference thereof, said ducts being formed from a corrosion-resistant metal.

References Cited in the file of this patent UNITED STATES PATENTS 719,382 Shaw et a1. Jan. 27, 1903 1,396,086 Anthony Nov. 8, 1921 FOREIGN PATENTS 163,782 Great Britain May 23, 1921 1,032,000 Germany June 12, 1958 

1. A GAS BURNER COMPRISING A COAXIALLY MOUNTED, NESTED SERIES OF SEPARABLE TUBULAR DUCTS OF GRADUATED DIAMETER INCLUDING AT LEAST A PRIMARY OXIDANT GAS DUCT, A SECONDARY OXIDANT GAS DUCT, A SAMPLE DUCT POSITIONED BETWEEN THE PRIMARY AND SECONDARY OXIDANT GAS DUCTS AND A FUEL GAS DUCT, EACH HAVING A DISCHARGE END AND A BASE END, SAID DUCTS BEING SPACED APART AT THEIR DISCHARGE ENDS AND FORMING A GRADUATED SERIES OF CONCENTRIC, ANNULAR DISCHARGE ORIFICES LYING IN SUBSTANTIALLY THE SAME PLANE ABOUT A CENTRALLY POSITIONED DISCHARGE ORIFICE, EACH OF SAID DUCTS BEING PROVIDED WITH AN INLET ORIFICE AT ITS BASE END FOR INTRODUCTION OF ONE OF SAID PRIMARY OXIDANT GAS, SAID SECONDARY OXIDANT GAS, SAID SAMPLE, AND SAID FUEL GAS, EACH OF SAID DUCTS OTHER THAN THE CENTRAL POSITIONED DUCT OF SAID SERIES BEING REMOVABLY MOUNTED AT ITS BASE END UPON THE BASE OF THE NEXT SMALLER DUCT IN THE SERIES, SAID DUCTS BEING FORMED FROM IMPACT-RESISTANT MATERIAL THAT IS RESISTANT TO CORROSION UNDER SERVICE CONDITIONS OF THE BURNER. 